BEIJING (AFP) - China's Xi Jinping will visit Seoul next week, both sides said on Friday, going to the South for his first presidential journey to the Korean peninsula as Beijing's frustrations mount with the nuclear-armed North and its confrontational young leader Kim Jong Un.

China is the North's key ally, energy provider and diplomatic protector, their ties sealed in the Korean War, and sees its neighbour as a buffer against finding US troops stationed on its own border. Beijing and Seoul only established diplomatic ties in 1992 after decades of Cold War hostility and suspicion, but it will be the second summit between Xi and South Korean President Park Geun-Hye, who visited China soon after she took office last year.

The July 3-4 visit will discuss "ways to cooperate on issues related to the situation on the Korean peninsula, including the North Korean nuclear issue", South Korea's presidential Blue House said in a statement.

Chinese foreign ministry spokesman Qin Gang told reporters it would cover "issues of common concern". On the other hand there has been no Chinese summit with the North since the death of its then leader Kim Jong-Il, Kim Jong Un's father, in December 2011.

Ahead of the announcement South Korea's Dong-A Ilbo newspaper called the trip "a message of considerable weight" to the North in an editorial. "It is significant, definitely, that Xi Jinping and Park have a very public, close relationship," Dr John Delury, an expert on China at Yonsei University in Seoul, said. "And the contrast with the fact that he hasn't even had his picture taken with Kim Jong-Un is starkly significant."

Mr Kim inherited the North Korean leadership from his father, becoming the third member of the Kim dynasty to rule the hermit state, and his reign has so far largely been seen as provocative, capricious and destabilising. He has had his own uncle Jang Song Thaek - seen as China's primary point of contact with the regime - executed in a purge, and threatened nuclear war against the US.

Pyongyang carried out its third underground atomic test in February 2013, resulting in fresh censure by the United Nations and a further headache for Beijing, which wants to restart stalled multilateral negotiations known as the six-party talks on the North's denuclearisation.

No visit by Mr Kim Jong Un to Beijing has ever been officially confirmed - although he is widely believed to have accompanied his father on a 2011 trip - while the last Chinese head of state to go to Pyongyang was Hu Jintao in 2005.

Mr Xi himself visited the North in 2008, when he was vice president, and the South 18 months later. But soon after becoming president last year, Mr Xi served the North notice that it no longer had a free pass.

Two months after Pyongyang's nuclear test sent tensions on the peninsula soaring, Xi cautioned against the sowing of "chaos for selfish gains". While he did not mention North Korea by name the remarks were widely seen as a slap.

The latest possible irritant came on Friday when the North's official news agency announced Mr Kim had observed the test-firing of a newly developed, high-precision tactical guided missile.

Seoul and Washington have persistently called on Beijing to exert more pressure on the North to abandon its nuclear weapons programme. But despite China's annoyance with North Korea, it fears the instability - and floods of refugees - that a collapse of the regime would bring and experts generally see little prospect of a total rupture.

Dr Sun Zhe, who teaches international relations at China's Tsinghua University, said Mr Xi was confronted with a "hard choice" on which of the Koreas to visit first. "China doesn't want to be an enemy of North Korea," Dr Sun said at a forum of scholars and experts in Beijing this week on China-South Korea relations. "We're still pushing baby Kim to have a dialogue," he added.

China's two-way trade with South Korea totalled US$274.24 billion last year, more than 40 times the US$6.55 billion recorded with the North. Yonsei University's Delury says Beijing has sought for two decades to maintain good relationships with both sides.

"North Korea is keeping China at arm's length to some degree," he said. "Xi Jinping is basically taking the opportunity... to ramp up the level of cooperation with South Korea, which is very much in line with China's interests, economic interests and diplomatic interests."

But Mr Chun Yung Woo, a former South Korean national security adviser and delegate to the six-party talks, warned bluntly that Pyongyang remains the biggest danger to Seoul-Beijing ties. "I think it's very important to manage risks which will come from North Korea in a way that does not harm our bilateral relationship," Mr Chun told Chinese scholars at the forum. "North Korea will continue to embarrass you, will continue to harm your interests, interests of regional peace and security."